RT Journal Article SR Electronic(1) A1 Cook, C. M. A1 Lanaras, T. A1 Wood, A. P. A1 Codd, G. A. A1 Kelly, D. P.YR 1991 T1 Kinetic properties of ribulose bisphosphate carboxylase/oxygenase from Thiobacillus thyasiris, the putative symbiont of Thyasira flexuosa (Montagu), a bivalve mussel JF Microbiology, VO 137 IS 7 SP 1491 OP 1496 DO https://doi.org/10.1099/00221287-137-7-1491 PB Microbiology Society, SN 1465-2080, AB Some kinetic properties of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase from Thiobacillus thyasiris, a marine, facultatively heterotrophic, sulphur-oxidizing bacterium and putative symbiont of Thyasira flexuosa (Montagu), a bivalve mussel, have been determined. The kinetic parameters for the CO2/Mg2+-activated enzyme were: K m(RuBP) 24·3 μm, K m(CO2) 125·5 μm, Km(O2) 900 μm and K m(Mg2+) 1·53 mm. The low CO2 affinity suggests that T. thyasiris may possess a CO2-concentrating mechanism. RuBP oxygenase activity was inhibited by increasing CO2 concentration. Divalent metal ions were essential for RuBP carboxylase activity; activity of the Mg2+-free enzyme could be restored by the addition of Mg2+, Mn2+ or Ca2+. The pH optimum was 7·8. The temperature optimum for RuBP carboxylase activity was 55 °C, although the enzyme rapidly lost activity at this temperature. An Arrhenius plot was biphasic, with a break at 40 °C. The activation energies were 55·5 × 103 J mol−1 and 32·9 × 103 J mol−1 over the temperature ranges 10–40 °C and 40–55 °C, respectively. Q 10 was 2·12 for any 10 °C increment between 10·40 °C, and 1·47 between 40·55 °C. RuBP carboxylase activity was stable at 35 °C, the optimum growth temperature of T. thyasiris and at 7·5 °C, the temperature of the habitat of Thyasira flexuosa, but the activity was 40% and 3·5%, respectively, of the potential activity at 55 °C. RuBP carboxylase activity was stimulated by NaCl concentrations of up to 0·3 m, with a maximum (33 %), occurring between 0·1 and 0·2 m-NaCl. At higher concentrations of NaG (>0·3 m) RuBP carboxylase activity was inhibited, UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-137-7-1491